Semiconductor device with gold bumps, and method and apparatus of producing the same

ABSTRACT

A semiconductor device comprises a semiconductor element having electrodes and metal bumps are attached to the electrodes. The metal bumps include copper cores and gold surface layers covering the cores. In addition, the metal bumps may include gold bump elements and solder bump elements connected together.

This application is a division of prior application Ser. No. 09/014,981,filed Jan. 28, 1998, now U.S. Pat. No. 6,333,554.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, a method ofproducing the same, and an apparatus for producing the same.

2. Description of the Related Art

With the progress in semiconductor integrated circuits in recent years,semiconductor elements having very many terminals (e.g., not less than300 terminals) have been placed in the market. Accordingly, it has beenstrongly demanded to improve the technology for connecting the terminals(electrodes) of a semiconductor element to the terminals (electrodes) ofa wiring board, and to reduce the cost.

Technology has been developed for connecting all the electrodes of thesemiconductor element to the electrodes of the wiring substrate at onetime by utilizing metal bumps. That is, metal bumps such as solder bumpsor gold bumps are first attached to the electrodes of the semiconductorelement, and the semiconductor element is pressed onto the wiring board,with its face directed downward, so that the metal bumps are joined tothe electrodes of the wiring board and the electrodes of thesemiconductor element are connected to the electrodes of the wiringboard.

The conductors of the integrated circuit of a semiconductor element areformed of aluminum and, hence, the electrodes of the semiconductorelements are generally formed of aluminum. On the other hand, theconductors of a wiring board are composed of copper and, hence, theelectrodes of the wiring board are generally formed of copper.

When solder bumps are to be used, a nickel layer and a titanium layerare formed on the aluminum electrodes of the semiconductor element andthe solder bumps are joined to the electrodes having a compositestructure of the semiconductor element, since solder joins poorly toaluminum. Thereafter, the semiconductor element is pressed onto thewiring board while being heated, so the solder bumps melt and spread onthe electrodes of the wiring board, with the result that the solderbumps are surely connected to the electrodes of the wiring board.

When gold bumps are to be used, there is no need to form a nickel layerand a titanium layer on the aluminum electrodes of the semiconductorelement unlike the case of using the solder bumps, since gold directlyjoins to aluminum. However, the gold bumps are attached to theelectrodes of the semiconductor element in the form of stud bumps withprojections, and, the semiconductor element is pressed onto the wiringboard while being heated after the surfaces of the stud bumps arelevelled, an electrically conducting adhesive is applied to the surfacesof the gold bumps, so that the gold bumps are connected to theelectrodes of the wiring board via the electrically conducting adhesive.The electrically conducting adhesive comprises a mixture of athermosetting resin and a metal filler mixed therein, and is thermallycured. Thereafter, the semiconductor element and the wiring board aresealed with a sealing adhesive (insulating resin) inserted therebetween.

When solder bumps are to be used, it is necessary to add the nickellayer and the titanium layer onto the aluminum electrodes of thesemiconductor element, as described above but not all users of thesemiconductor elements are necessarily allowed to apply the nickel layerand the titanium layer as desired, since application of the nickel layerand the titanium layer requires a special facility such as a vacuumchamber. Therefore, the solder bumps often cannot be used when asemiconductor element without a nickel layer and a titanium layer ispurchased.

When an electrically conducting adhesive is applied to the gold bumpsformed as stud bumps., on the other hand, the levelled surfaces of thestud bumps are not necessarily in parallel with the surface of thewiring circuit. Therefore, electric connection is not accomplished to asufficient degree despite using the electrically conducting adhesive,and the reliability of connection remains low. Moreover, the materialsare used in increased amounts, the steps of production are complex, andthe heating must be continued until the resin is cured, hindering theproductivity. Besides, in the case where the semiconductor element isdefective or the mounting thereof is defective, the semiconductorelement must be replaced by peeling the electrically conducting adhesiveoff the electrodes of the wiring board. However, it is difficult to peelit off after it is once thermally cured, since the electricallyconducting adhesive contains a thermosetting resin. This makes it verydifficult to repair the semiconductor element or the wiring board.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a semiconductordevice, and a method and an apparatus for producing the same whichpermit a semiconductor element to be mounted to a wiring board by aface-down technique, and to provide improved reliability of connectionsand simplicity of replacement of the semiconductor element.

A semiconductor device, according to the first feature of the presentinvention, comprises a semiconductor element having electrodes, andmetal bumps including cores and metal surface layers covering saidcores, said metal bumps being attached to the electrodes of saidsemiconductor element.

In this case, preferably, the metal surface layers comprise one of goldand solder.

Moreover, the metal surface layer is a plated layer plated on said core.The core comprises one of a metal, an inorganic material and an organicmaterial and has a diameter of not larger than 100 μm, and the metalsurface layer has a thickness of not larger than 50 μm. There is furtherprovided a wiring board having electrodes, metal bumps attached to theelectrodes of said semiconductor element being connected to theelectrodes of the wiring board.

A semiconductor device, according to the second feature of the presentinvention, comprises a semiconductor element having electrodes, andmetal bumps comprising gold bump elements and solder bump elementsconnected together, said gold bump elements being attached to theelectrodes of said semiconductor element.

In this case, preferably, the gold bump element has a first side and asecond side opposite to said first side, the first side of said goldbump element being joined to the electrode of the semiconductor element,and the second side of said gold bump element is joined to said solderbump element. The second side of said gold bump element forms a flatsurface or a flat surface with a recessed portion. There is furtherprovided a wiring board having electrodes, the metal bumps beingattached to the electrodes of said semiconductor element are connectedto the electrodes of said wiring board.

A semiconductor device, according to the third feature of the presentinvention, comprises a semiconductor element having electrodes, andmetal bumps comprising gold-containing solder films formed on theelectrodes of said semiconductor element and metal bump elementsprovided on said gold-containing solder films.

In this case, preferably, there is further provided a wiring boardhaving electrodes, the metal bumps attached to the electrodes of saidsemiconductor element being connected to the electrodes of said wiringboard. The metal bump element comprises one of gold and solder. Themetal bump element is formed as one of a metal film and a metal ball.

A method of producing a semiconductor device, according to the fourthfeature of the present invention, comprises the steps of immersing asemiconductor element having electrodes in a molten gold-containingsolder to form gold-containing solder films on the electrodes of saidsemiconductor element, and forming metal bump elements on saidgold-containing solder films to thereby form metal bumps comprising saidgold-containing solder films and said metal bump elements.

In this case, preferably, the step of forming the metal bump elements onsaid gold-containing solder films comprises immersing thegold-containing solder films in the molten solder to form solder films.The step of forming the metal bump elements on said gold-containingsolder films comprises immersing the gold-containing solder films in abath of a molten metal. The step of forming the metal bump elements onsaid gold-containing solder films comprises joining solid pieces ontothe gold-containing solder films.

A method of producing a semiconductor device, according to the fifthfeature of the present invention, comprises the steps of performing aprocess for imparting a fluxing action to the electrodes of thesemiconductor element prior to immersing the semiconductor elementhaving the electrodes in the molten gold-containing solder.

In this case, preferably, the process for imparting said fluxing actioncomprises irradiating the semiconductor element with a plasma. The stepof performing the process for imparting said fluxing action comprisescleaning the electrodes of the semiconductor element with a first gas,and forming a compound of a material of the electrodes of thesemiconductor element and of a second gas.

A semiconductor device, according to the sixth feature of the presentinvention, comprises a semiconductor element having electrodes, andmetal bumps including gold bump elements having nose-like projectionsprovided on the electrodes of said semiconductor element and solderelements formed on said gold bump elements to cover said projections.

In this case, preferably, there is further provided a wiring boardhaving electrodes, the metal bumps attached to the electrodes of saidsemiconductor element being connected to the electrodes of the wiringboard.

A semiconductor device, according to the seventh feature of the presentinvention, comprises a semiconductor element having electrodes, andmetal bumps including gold bump elements provided on the electrodes ofsaid semiconductor element and first metal layers formed around saidgold bump elements to protect said gold bump elements.

In this case, preferably, the first metal layer has a melting pointlower than a melting point of said gold bump element. A second metallayer is formed around said first metal layer. The second metal layerhas a melting point which is lower than a melting point of said firstmetal layer by more than 20° C. There is further provided a wiring boardhaving electrodes, the metal bumps attached to the electrodes of saidsemiconductor element being connected to the electrodes of the wiringboard.

A method of producing semiconductor devices, according to the eighthfeature of the present invention, comprises the steps of attaching goldbump elements to electrodes of a semiconductor element, immersing saidsemiconductor element in a bath containing a molten amalgam of a mixtureof a metal for protecting gold and mercury to form an amalgam layer onsaid gold bump elements, heating said semiconductor elements to vaporizemercury in the amalgam and to form metal films on the gold bump elementsto protect gold, and transferring molten solder elements to said metalfilms.

A method of producing semiconductor devices, according to the ninthfeature of the present invention, comprises the step of attaching goldbump elements to electrodes of a semiconductor element and transferringmolten solder elements to said gold bump elements in an environmentcontaining inert gas at an oxygen concentration of not larger than10,000 ppm.

In this case, preferably, at least one of alcohol, ketone, ester, etherand a mixture thereof is used as a fluxing agent for transferring priorto transferring the molten solder elements. The fluxing agent fortransferring comprises a flux obtained by mixing a solid componentthereof in an amount of not larger than 10% by weight in an alcohol.

An apparatus for producing semiconductor devices, according to the tenthfeature of the present invention, comprises a booth, a molten-soldervessel arranged in said booth so that gold bump elements provided on theelectrodes of a semiconductor element can be immersed in said vessel,means for supplying inert gas into said booth, and means for detectingthe oxygen concentration in said booth.

In this case, preferably, provision is further made of a flux vessel fortransfer disposed in said booth. There are further provided amolten-solder vessel, arranged so that gold bump elements provided onthe electrodes of a semiconductor element can be immersed in saidvessel, and a support structure, for hanging said semiconductor element,said support structure including a hanging mechanism comprising at leasttwo mutually movably coupled coupling members. The above-mentioned atleast two coupling members comprises members that are coupled togetherlike a chain.

An apparatus for producing semiconductor devices, according to theeleventh feature of the present invention, comprises a molten-soldervessel arranged so that gold bump elements provided on the electrodes ofa semiconductor element can be immersed in said vessel, and a supportstructure for hanging said semiconductor element, said support structureincluding a pump-type adsorption head having an open suction hole forholding the semiconductor element.

An apparatus for producing semiconductor devices, according to thetwelfth feature of the present invention, comprises a molten-soldervessel arranged so that gold bump elements provided on the electrodes ofa semiconductor element can be immersed in said vessel, and a supportstructure for hanging said semiconductor element, said support structureincluding a hanging mechanism comprising at least two mutually movablycoupled coupling members and a pump-type adsorption head having an opensuction hole for holding the semiconductor element.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail in the followingdescription of the preferred embodiments, with reference to theaccompanying drawings in which:

FIG. 1 is a cross-sectional view of a portion of the semiconductordevice according to the first embodiment of the present invention;

FIG. 2 is a cross-sectional view of the semiconductor element of FIG. 1mounted to a circuit board;

FIGS. 3A to 3D are views illustrating the process in which the surfacelayers around the cores are subjected to a electroless plating;

FIGS. 4A to 4C are views illustrating the process in which bumpscomprising cores and surface layers are attached to the electrodes ofthe semiconductor element and the semiconductor element is then mountedto the wiring board;

FIG. 5 is a view illustrating a modified example of the semiconductordevice of FIG. 2;

FIG. 6 is a view illustrating another modified example of thesemiconductor device of FIG. 2;

FIG. 7 is a view illustrating how to apply an electrically conductingadhesive to the surfaces of the metal bumps attached to the electrodesof the semiconductor element;

FIG. 8 is a cross-sectional view of the semiconductor device accordingto the second embodiment of the present invention;

FIG. 9 is a cross-sectional view of the semiconductor element of FIG. 8mounted to the circuit board;

FIG. 10 is a cross-sectional view of the semiconductor device accordingto the third embodiment of the present invention;

FIG. 11 is a view illustrating a modified example of the semiconductordevice of FIG. 10;

FIGS. 12A to 12C are views illustrating the process for producing thesemiconductor device of FIG. 10;

FIGS. 13A to 13D are views illustrating the semiconductor deviceaccording to the fourth embodiment of the present invention;

FIGS. 14A to 14D are views illustrating a modified example of thesemiconductor device of FIGS. 13A to 13D;

FIG. 15 is a cross-sectional view of the semiconductor device accordingto the fifth embodiment of the present invention;

FIG. 16 is a view of the metal bump of FIG. 15 when the end thereof isflattened;

FIG. 17 is a cross-sectional view of the semiconductor device accordingto the sixth embodiment of the present invention;

FIG. 18 is a cross-sectional view of the semiconductor device accordingto the seventh embodiment of the present invention;

FIGS. 19A to 19D are views illustrating the semiconductor deviceaccording to the eighth embodiment of the present invention;

FIG. 20 is a view illustrating the apparatus for producing semiconductordevices according to the ninth embodiment of the present invention;

FIG. 21 is a view illustrating the apparatus for producing semiconductordevices according to the tenth embodiment of the present invention;

FIG. 22 is a view illustrating an example in which the apparatus of FIG.21 includes a plurality of molten-solder vessels and a fluxing agentvessel in the booth;

FIG. 23 is a view illustrating a feature of the suction support devicein the apparatuses of FIGS. 20 and 21;

FIG. 24 is a view illustrating a modified example of the hangingmechanism;

FIG. 25 is a view illustrating another modified example of the hangingmechanism;

FIG. 26 is a view illustrating a further modified example of the hangingmechanism;

FIG. 27 is a cross-sectional view illustrating an example of thepump-type suction head;

FIG. 28 is a side view of the suction head of FIG. 27;

FIG. 29 is a cross-sectional view of the suction head of FIG. 27 withthe semiconductor element supported thereby;

FIG. 30 is a view illustrating a modified example of the suction supportdevice;

FIG. 31 is a view illustrating another modified example of the suctionsupport device;

FIG. 32 is a view illustrating a further modified example of the suctionsupport device;

FIG. 33 is a view illustrating a step in a process for forming solderbump elements on the gold bump elements by vaporization; and

FIG. 34 is a view illustrating a step that follows the step of FIG. 33.

DETAILED EXPLANATION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show the semiconductor device according to the firstembodiment of the present invention. In FIG. 1, the semiconductor device10 comprises a semiconductor element 12 having electrodes 14 and metalbumps 16 attached to the electrodes 14.

The metal bump 16 comprises a core 18 in the form of a ball and asurface layer 20 surrounding the core 18. The semiconductor element 12is a bare chip constituting a semiconductor integrated circuit, andincludes an integrated circuit (not shown) and a conductor 12 aconnected to the integrated circuit. The electrode 14 is connected tothe conductor 12 a. Note that FIG. 1 shows one electrode 14 and onemetal bump 16 only, but it is needless to say that a plurality ofelectrodes 14 and metal bumps 16 are provided according to the number ofterminals of the semiconductor element 12. This also applies to thesubsequent embodiments.

In FIG. 2, the semiconductor device 10 includes a wiring board 22 havingelectrodes 24, in addition to the constitution of FIG. 1. The electrodes24 of the wiring board 22 are connected to a circuit pattern (not shown)in the wiring board 22, and are disposed in the same arrangement as theelectrodes 14 of the semiconductor element 12. The metal bumps 16attached to the electrodes 14 of the semiconductor element 12 areconnected to the electrodes 24 of the wiring board 22, by pressing thesemiconductor element 12 onto the wiring board 22 in a face-down bondingmethod while being heated. In this embodiment, the metal bumps 16 aredirectly joined to the electrodes 24 of the wiring board 22. It istherefore possible to remove the semiconductor element 12 from thewiring board 22 to repair it. Space between the semiconductor element 12and the wiring board 22 is filled with an adhesive 26 for fixing. Theadhesive (insulating resin) 26 for fixing can be applied to the wiringboard 22 in advance as shown in FIG. 4(C) or can be charged after thesemiconductor element 12 is pressed onto the wiring board 22.

The electrodes 14 of the semiconductor element 12 are made of aluminumand the electrodes 24 of the wiring board 22 are made of copper. In theembodiment of FIGS. 1 and 2, the core 18 of the metal bump 16 is made ofcopper and has a diameter of 100 μm, and the surface layer 20 is made ofgold and has a thickness of 10 μm.

The surface layer 20 is formed around the core 18 by electrolessplating, as shown in FIGS. 3A to 3D. FIG. 3A shows the step in which thecopper cores 18 contained in a container 28 are washed. The washing iseffected twice. The cores 18 are washed first with an aqueous solutionof hydrochloric acid and then with pure water. FIG. 3B shows the step inwhich the cores 18 contained in the container 28 are subjected to anelectroless plating in a plating vessel 30. The plating vessel 30contains a electroless plating solution including gold. The electrolessplating is suited for plating the cores 18 that are small solid pieces,since no current needs be supplied to the cores 18. FIG. 3C shows thestep in which the metal bumps 16 comprising copper cores 18 plated withthe gold surface layer 20 are being washed. The washing is effectedtwice. The metal bumps 16 are washed first with pure water and then withacetone. FIG. 3D shows the step in which the metal bumps 16 are driedwith vacuum in a vacuum vessel 32. The thus formed metal bumps 16 arestored in a suitable container and are then attached to the electrodes14 of the semiconductor element 12.

FIGS. 4A to 4C show the steps in which metal bumps 16 comprising thecores 18 and the surface layers 20 are attached to the electrodes 14 ofthe semiconductor element 12, and the semiconductor element 12 is thenmounted to the wiring board 22. FIG. 4A illustrates the step in whichthe metal bumps 16 in the container 34 are attracted and held by suctionholes 36 a of a suction head 36. FIG. 4B illustrates the step in whichthe suction head 36 is pressed onto the semiconductor element 12 whilebeing heated. The suction holes 36 a are disposed in the samearrangement as the electrodes 14 of the semiconductor element 12 and,hence, the metal bumps 16 having the gold surface layer 20 are joined tothe electrodes 14 of the semiconductor element 12. When the suction head36 is then separated from the semiconductor element 12, the metal bumps16 are transferred to the electrodes 14 of the semiconductor element 12.This condition is shown in FIG. 1.

FIG. 4C illustrates the step in which the semiconductor element 12 ispressed onto the wiring board 22 while being heated. The metal bumps 16attached to the electrodes 14 of the semiconductor element 12 are joinedto the electrodes 24 of the wiring board 22. The adhesive 26 for fixingcauses the semiconductor element 12 and the wiring board 22 to beadhered together. This condition is shown in FIG. 2.

If the shape and the size of the cores 18 of the metal bumps 16 areconstant, those of the metal bumps 16 having the surface layers 20covering the cores 18 are constant. The cores 18 in the metal bumps 16are made of a material harder than the surface layers 20 and, hence, themetal bumps 16 are maintained in a substantially constant shape. Thesurface layers 20 are soft and they extend along the electrodes 24 whenthey are joined to the electrodes 24 of the wiring board 22 to therebyassure a sufficient contact area for the electrodes 24 and to accomplishgood electric connection. The core 18 is preferably made of a materialinto which copper or aluminum, which is the material of the electrodes,diffuses less than it does into the surface layer 20, to thereby preventthe metal bump 16 from being alloy and from becoming brittle. Thesurface layer 20 is preferably made of a material into which thematerial for the electrode easily diffuses, so that an alloy layer isformed in the joined portion between the electrode and the metal bump tothereby realize a mechanically and electrically favorable connection.

It is preferable that the cores 18 are formed in the form of the ballshaving a diameter of not larger than 100 μm arid the surface layers 20have a thickness of not larger than 50 μm. The cores 18 may be formed ofa metal other than copper, such as nickel, silver or bismuth. Or, thecores 18 may be formed of a ball of an inorganic material such asalumina or silica, or of an organic material such as PTFE or nylon. Thesurface layers 20 may be formed of gold or a metal comprising gold andother elements added to gold. In the above-mentioned embodiment, thesurface layer 20 are formed by electroless plating to cover the core 18.However, the surface layers 20 may be formed by electrolytic plating orhot dipping.

FIGS. 5 and 6 illustrate modified examples of the semiconductor deviceof FIG. 2. The example of FIG. 5 is the same as the example of FIG. 2except that an electrically conducting adhesive 38 is interposed betweenthe metal bumps 16 and the electrodes 24 of the wiring board 22. Theelectrically conducting adhesive 38 comprises a thermosetting resin anda metal filler (gold, silver, palladium, etc.) mixed therein, and isthermally cured.

The example of FIG. 6 is the same as the example of FIG. 2 except that asolder layer 40 is interposed between the metal bumps 16 and theelectrodes 24 of the wiring board 22. Even when the solder layer 40 isbeing formed, it is possible to remove the semiconductor element 12 fromthe wiring board 22 to repair it.

FIG. 7 illustrates an example in which the electrically conductingadhesive 38 (FIG. 5) is applied to the surfaces of the metal bumps 16mounted on the electrodes 14 of the semiconductor element 12. The metalbumps 16 are pressed onto a glass plate or the like to flatten or levelthe surfaces of the metal bumps 16, and the ends of the metal bumps 16are then immersed in the electrically conducting adhesive in theelectrically conducting adhesive vessel 39, to thereby apply theelectrically conducting adhesive 38 onto the surfaces of the metal bumps16. Thus, the metal bumps 16 to which the electrically conductingadhesive 38 is applied are connected to the electrodes 24 of the wiringboard 22.

FIGS. 8 and 9 illustrate the semiconductor device according to thesecond embodiment of the present invention. Like in the embodiment ofFIGS. 1 and 2, the semiconductor device 10 according to this embodimentcomprises a semiconductor element 12 having electrodes 14, metal bumps16 attached to the electrodes 14, and a wiring board 22 havingelectrodes 24. The metal bump 16 comprises a spherical core 18 and asurface layer 20 a covering the core 18.

In this embodiment, the electrodes 14 of the semiconductor element 12are formed of aluminum, and a solder-plated layer 42 is formed thereon.The electrodes 24 of the wiring board 22 are formed of copper. The core18 of the metal bump 16 is formed of copper and has a diameter of 100μm, and the surface layer 20 a is formed of a solder and has a thicknessof 10 μm. The solder surface layer 20 a is formed by electroless platinglike the gold surface layer 20.

The metal bumps 16 having the solder surface layer 20 a can be easilyjoined to the electrodes 14 having the solder-plated layer 42, by usingthe suction head 36 shown in FIG. 4. Unlike the nickel layer or thetitanium layer, the solder-plated layer 42 can be formed relativelyeasily. Upon pressing the semiconductor element 12 onto the wiring board22 while being heated, the metal bumps 16 attached to the electrodes 14of the semiconductor element 12 are easily joined to the electrodes 24of the wiring board 22.

In this case too, if the shape and the size of the cores 18 of the metalbump 16 are constant, those of the metal bumps 16 having the surfacelayers 20 a covering the cores 18 are constant. The cores 18 in themetal bump 16 are made of a material harder than the surface layers 20 aand, hence, the metal bumps 16 can maintain a substantiallypredetermined shape. The surface layers 20 a are soft, and extend alongthe electrode 24 when they are joined to the electrodes 24 of the wiringboard 22, to assure a sufficient contact area for the electrodes 24 andto accomplish a favorable electrical connection.

The core 18 has a diameter which is not larger than 100 μm, and can bemade of a ball of a metal other than copper such as nickel, silver orbismuth, or of an inorganic material such as alumina or silica, or of anorganic material such as PTFE or nylon. The surface layer 20 a has athickness of not larger than 50 μm, and can be formed not only byelectroless plating, but also by electrolytic plating or hot dipping.The solder forming the surface layer 20 a is a brazing materialcomprising a single metal or an alloy having a melting point of nothigher than 400° C., and can be selected, for example, from Sn—Bi—Ag,Sn—In, In, and the like.

FIG. 10 illustrates the semiconductor device according to the thirdembodiment of the present invention. The semiconductor device 10comprises a semiconductor element 12 having electrodes 14, and metalbumps 16 comprising gold bump elements 44 and solder bump elements 46that are connected together, the gold bump elements 44 being attached tothe electrodes 14 of the semiconductor element 12. As in the embodimentof FIGS. 2, 5 and 6, it is obvious that the semiconductor device 10 mayinclude the wiring board 22 that is attached to the semiconductorelement 12 via the metal bumps 16. The wiring board 22 has electrodes 24to be connected to the electrodes 14 of the semiconductor element 12. Inthis and the subsequent embodiments, even when the wiring board 22 isnot shown, it should be noted that the semiconductor device 10 includesthe wiring board 22 as in the embodiment of FIGS. 2, 5 and 6.

In FIG. 10, the gold bump elements 44 are formed approximately in asemi-spherical shape, and have a recessed portion formed in the flatsurfaces thereof. The spherical side of the gold bump element 44 isjoined to the electrode 14 of the semiconductor element 12, and the flatsurface side of the gold bump element 44 is joined to the solder bumpelement 46. That is, the ball-like solder bump element 46 is fitted tothe recessed portion in the flat surface of the gold bump element 44.

According to this constitution, the gold bump elements 44 can be easilyjoined to the electrodes 14 of the semiconductor element 12, and thesolder bump elements 46 can be easily joined to the electrodes 24 of thewiring board 22. It is further allowed to precisely control the amountof the solder bump elements 46 so that they can be reliably joined tothe electrodes 24 of the wiring board 22. The solder bump elements 46are composed of a brazing material of a single metal or an alloy havinga melting point of not higher than 400° C., and is selected, forexample, from Sn—Bi—Ag, Sn—In, In, and the like. The solder bumpelements 46 may have a diameter of not larger-than 100 μm.

FIGS. 12A to 12C illustrate the steps for producing the semiconductordevice 10 of FIG. 10. In FIG. 12A, ball-like gold bump elements 44 areprepared and attached and held by the suction head 36, which is similarto the suction head 36 of FIG. 4. The ball-like gold bump elements 44held by the suction head 36 are transferred to the electrodes 14 of thesemiconductor element 12. In FIG. 12B, a tool 48 is used for flatteningthe gold bump elements 44 and for forming recessed portions. The tool 48has a surface shape corresponding to the flat surfaces and the recessedportions of the gold bump elements 44. The tool 48 is pressed onto thegold bump elements 44 attached to the electrodes 14 of the semiconductorelement 12. Referring to FIG. 12C, the gold bump elements 44 have ashape with a flat surface and a recessed portion. By using the suctionhead 36, the solder bump elements 46 held by the suction head 36 aretransferred and adhered to the recessed portions of the gold bumpelements 44.

FIG. 11 illustrates a modified example of the semiconductor device ofFIG. 10. The semiconductor device 10 comprises a semiconductor element12 having electrodes 14, and metal bumps 16 comprising gold bumpelements 44 and solder bump elements 46 that are connected together, thegold bump elements 44 being attached to the electrodes 14 of thesemiconductor element 12. In this example, the shape of the gold bumpelements 44 and the solder bump elements 46 is varied. The gold bumpelements 44 are formed in a cylindrical shape and have a recessedportion formed in the flat surfaces thereof. The solder bump elements 46are formed in a semi-circular shape, and portions including flatsurfaces are fitted in the recessed portions formed in the flat surfacesof the gold bump elements 44.

The shape of the gold bump elements 44 and the solder bump elements 46is not limited to those Illustrated in the drawings. For example, thegold bump elements 44 can be formed in the shape of a flat plate. Thesolder bump elements 46 may be formed as pellets of various shapes. Thesolder bump elements may be attached to the gold bump elements 44 bymelt immersion transfer or vaporization.

FIGS. 13A to 13D illustrate the semiconductor device according to thefourth embodiment of the present invention. In this embodiment, thesemiconductor element 12 having electrodes 14 is irradiated with plasmaP, as shown in FIG. 13A. First, the semiconductor element is irradiatedwith the plasma for 5 minutes while oxygen (O₂) is supplied. Thus,impurities such as carbon and the like are removed from the surfaces ofthe electrodes 14. Then, the semiconductor element is irradiated withthe plasma for 5 minutes while argon (Ar) is supplied. Thus, the surfaceoxide films are removed from the electrodes 14. The semiconductorelement is then irradiated with the plasma for 5 minutes while supplyingCF4 ₄. Thus, a compound of aluminum and fluorine is formed on thesurfaces of the electrodes 14, this compound working as a flux for thesolder. During this period, an electric power of 10 watts is supplied.Instead of this processing, the electrodes 14 may be coated with afluxing agent (organic acid, halogen-containing compound, etc.).

Referring to FIG. 13B, the semiconductor element 12 is immersed in agold-containing solder vessel 50 which contains a molten gold-containingsolder. The gold-containing solder is an alloy obtained by adding one ormore elements to gold and has a melting point of not higher than 400°C., and is selected from, for example, Au—Sn, Au—Ge, Au—Si, and thelike. This embodiment uses an Au-20%Sn solder. Then, as shown in FIG.13C, gold-containing solder films 52 are formed on the electrodes 14 ofthe semiconductor element 12. The gold-containing solder films 52 are onthe aluminum electrodes 14 and have a property in which they are easilywetted by the solder.

Referring to FIG. 13C, the semiconductor element 12 is immersed in asolder vessel 54 which contains a molten solder having a low meltingpoint. This embodiment uses a bath of a low-melting molten Sn—Bi—1%Agsolder. Then, as shown in FIG. 13D, solder elements 56 are formed on thegold-containing solder films 52 on the electrodes 14 of thesemiconductor element 12. The solder elements 56 are films of solder.The solder elements 56 may be formed by vaporization. Thus, the metalbumps 16 are formed by the gold-containing solder films 52 and thesolder elements 56. Then, as shown in FIG. 13D, the semiconductorelement 12 is pressed onto the wiring board 22 while being heated by theface-down bonding method, so that the metal bumps 16 attached to theelectrodes 14 of the semiconductor element 12 are easily joined to theelectrodes 24 of the wiring board 22.

FIGS. 14A to 14D illustrate a modified example of the semiconductordevice of FIGS. 13A to 13D. Referring to FIG. 14A, the semiconductorelement 12 having electrodes 14 is irradiated with a plasma P whileoxygen, argon and CF₄ are supplied. Referring to FIG. 14B, thesemiconductor element 12 is immersed in the gold-containing solder.vessel 50. Then, as shown in FIG. 14C, gold-containing solder films 52are formed on the electrodes 14 of the semiconductor element 12. In FIG.14C, solder elements 56 a are formed on the gold-containing solder films52 on the electrodes 14 of the semiconductor element 12.

The solder elements 56 a are solder balls which can be transferred byusing, for example, the suction head 36 of FIG. 4. Here, the solderelements 56 a are not limited to the solder balls but may assume anyform. Thus, the metal bumps 16 are formed by the gold-containing solderfilm 52 and the solder elements 56 a. Referring to FIG. 14D, thesemiconductor element 12 is then pressed onto the wiring board 22 whilebeing heated by the face-down bonding method, whereby the metal bumps 16attached to the electrodes 14 of the semiconductor element 12 are easilyJoined to the electrodes 24 of the wiring board 22.

In FIGS. 13 and 14, the solder elements 56, 56 a are formed on thegold-containing solder films 52. It is, however, also possible to use agold film, gold balls or any other bump elements instead of the solderelements 56, 56 a.

FIG. 15 illustrates the semiconductor device according to the fifthembodiment of the present invention. In this embodiment, thesemiconductor device 10 comprises a semiconductor element 12 havingelectrodes 14, and metal bumps 16, including gold bump elements 58,having nose-like projections 58 a formed on the electrodes 14 of thesemiconductor element 12 and solder elements 60 formed on the gold bumpelements 58 so as to cover the projections 58 a. This semiconductordevice 10 may also include the wiring board 22 having electrodes 24 towhich the metal bumps 16 will be connected, similar to that of theaforementioned embodiments.

Gold bump elements 58 known as stud bumps have been obtained by bondinga gold wire onto the electrodes 14 by using a capillary. The solderelements 60 are formed by immersing the gold bump elements in a moltensolder. Thus, the metal bumps 16 are obtained having the solder elements60 added to the conventional stud bumps. The solder elements 60 arejoined to the electrodes 24 of the wiring board 22 without forming gap.Desirably, the bottom of the gold bump elements 58 has a diameter “a”equal to the height “b” of the gold bump elements 58, and the solderelements 60 are adhered up to the tip of nose-like projection of thegold bump elements 58.

FIG. 16 illustrates the metal bump where the tip of the metal bump 16 ofFIG. 15 is pressed onto a flat surface such as of a glass plate and isflattened. The metal bump 16 can be attached in this state to theelectrode 24 of the wiring board 22.

FIG. 17 illustrates the semiconductor device according to the sixthembodiment of the present invention. In this embodiment, thesemiconductor device 10 comprises a semiconductor element 12 havingelectrodes 14, and metal bumps 16, including gold bump elements 62,provided on the electrodes 14 of the semiconductor element 12 and afirst metal layers 64 covering the gold bump elements 62 to protect thegold bump elements 62.

It is desirable that the first metal layers 64 are composed of a solderhaving a property for suppressing the diffusion of gold. As describedearlier, the solder is a brazing material of a single metal or an alloyhaving a melting point which is not higher than 400° C. The soldersuited for suppressing the diffusion of gold may be indium (In, m.p.,280° C.), an Au-20%Sn alloy (m.p., 280° C.) or the like.

The first metal layer 64 may be composed of a barrier metal which reactspoorly with gold. Examples of the metal that reacts poorly with goldinclude Bi, Ni, Zn, Cd, Cr, Ge, Ga and the like. Thus, by providing thefirst metal layer 64 to surround the gold bump elements 62, the metalbump elements 62 work stably for extended periods of time, and the metalbumps 16 exhibit improved reliability.

FIG. 18 illustrates the semiconductor device according to the seventhembodiment of the present invention. In this embodiment, second metallayers 66 are further provided to cover the first metal layers 64 ofFIG. 17. The first metal layers 64 work to protect the gold bumpelements 62, whereas the second metal layers 66 are composed of a solderthat can easily wet copper. When the semiconductor element 12 is mountedto the wiring board 22, therefore, the second metal layers 66 are morereliably joined to the copper electrodes 24 of the wiring board 22.

The combinations of the first metal layers 64 having a property forsuppressing the diffusion of gold and the second metal layer 66 that caneasily wet copper are described in the following example 1.

EXAMPLE 1

Combinations (a) (b) (c) (d) First metal layer 64 In In Au-20% Sn InSecond metal layer In—Sn Sn—Bi-1% Ag Sn—Bi-1% Ag In—Ag 66

The combinations of the first metal layers 64 having poor reactivitywith gold and the second metal layers 66 that can easily wet copper aredescribed in the following example 2.

EXAMPLE 2

Combinations (a) (b) First metal layer 64 Bi Ni Second metal layer 66In—Sn Sn—Pb—In

In these examples, indium has a melting point of 157° C., Au-20%Sn has amelting point of 280° C., In—Sn eutectic crystal has a melting point of117° C., Sn—Bi—1%Ag has a melting point of 139° C., and Sn—Pb—In has amelting point of 162° C. Bi and Ni have thicknesses of about 5000angstroms. The tin described in the following Example 3 has a meltingpoint of 232° C.

In addition, the first metal layer 64 and the second metal layer 66 canbe formed by a melting-transferring. In this case, it is desired thatthe melting point of the second metal layer 66 is lower than the meltingpoint of the first metal layer 64 by more than 20° C. When thetemperature difference is not larger than 20°C., the first metal layer64 and the second metal layer 66 are melted in the molten vessel at thetime of melting-transferring of the second metal layer 66, and thesecond metal layer 66 is not properly transferred onto the first metallayer 64. Example 3 satisfies these conditions.

EXAMPLE 3

Combinations (a) (b) First metal layer 64 In Sn Second metal layer 66In—Sn Sn—Pb—In Difference in m.p. 40° C. 70° C.

FIGS. 19A to 19D illustrate an eighth embodiment of the presentinvention. The semiconductor device 10 has, like the above-mentionedembodiment, metal bumps comprising gold bump elements 62, first metallayers 70 and second metal layers 74. This embodiment is concerned witha method of producing the semiconductor device of this type.

In FIG. 19A, the gold bumps 62 are attached to the electrodes 14 of thesemiconductor element 12, and the semiconductor element 12 is immersedin the vessel 68 containing a molten amalgam comprising a mixture of ametal for protecting gold and mercury, in order to form an amalgamlayer. Here, silver, that poorly reacts with gold, is selected as ametal for protecting gold. Silver and mercury are mixed together to forman amalgam (Hg+Ag).

In FIG. 19B, the semiconductor element 12 is heated to vaporize mercuryin the amalgam (Hg+Au) to thereby form gold films 70 on the gold bumpelements 62 to protect the gold. In FIG. 19C, the semiconductor element12 is immersed in a vessel 72 containing a molten solder. As shown inFIG. 19D, therefore, the solder elements 74 are melted and transferredonto the metal film 70. By using the thus formed metal bumps, thesemiconductor element 12 is mounted on the wiring board 22.

FIG. 20 illustrates the ninth embodiment of the present invention. Thisembodiment illustrates an apparatus and a method for producingsemiconductor devices and, particularly, a melting-transferringapparatus used for melting and transferring solder films onto the goldbump elements 62 in the apparatus for producing semiconductor devices inthe embodiments described above.

The apparatus 80 for producing semiconductor devices comprises a booth82, a molten-solder vessel 84 in which the gold bump elements 62provided on the electrodes of the semiconductor element 12 can beimmersed, means 86 for supplying an inert gas into the booth 82, andmeans 88 for detecting the oxygen concentration in the booth 82. Thesemiconductor element 12 is supported in the booth 80 by a suctionsupport device 90. The suction support device 90 includes a heater andhas a function for conveying the semiconductor element 12. Themolten-solder vessel 84 is placed on a table 91 which includes a heater.

Means 86 for supplying an inert gas is connected to the booth 82 througha duct 92 which is provided with a gas-pressure buffer tube 94. Nitrogengas or Argon gas is used as the inert gas. The oxygen concentration inthe booth 82 decreases as the inert gas is introduced into the booth 82.The oxygen concentration detecting means 88 detects the oxygenconcentration in the booth 82. The molten solder in the molten-soldervessel 84 is melted and transferred onto the gold bump elements 62 in anenvironment where the detected oxygen concentration that is lower than10000 ppm.

The molten solder in the molten-solder vessel 84 is melted andtransferred to the gold bump elements 62 in the environment in which theoxygen concentration is not higher than 10000 ppm, as described above,so that the solder films having an approximately uniform thickness areformed on the gold bump elements 62. If the oxygen concentration ishigher, the molten solder is oxidized, the surface of the solder issolidified, and it becomes no longer possible to form solder filmshaving a uniform thickness on the gold bump elements 62. It is,therefore, desired that the molten solder in the molten-solder vessel 84is melted and transferred onto the gold bump elements 62 in theenvironment in which the oxygen concentration is not higher than 10000ppm.

It is further desirable to use at least one of alcohol, ketone, ester,ether or a mixture thereof as a flux for transfer prior to melting andtransferring the molten solder onto the gold bump elements 62. The fluxmay have a low viscosity or a high viscosity. As the flux material fortransfer, the following can be used. An alcohol such as methanol,ethanol, propanol, isopropanol, butanol, or polyethylene glycol (m.w.400); a ketone such as acetone, dimethyl ketone, or ethyl methyl ketone;an ester such as ethylene glycol monoacetate, ethylene glycol diacetate,propylene glycol monoacetate or propylene glycol diacetate; or an ethersuch as ethylene glycol dimethyl ether, ethylene glycol diethyl ether,ethylene glycol dibutyl ether, or diethylene glycol dimethyl ether.

The combinations that can be used are as follows.

(a) 100% by weight of ethanol.

(b) Ethanol residue+0.2% by weight of polyethylene glycol.

(c) Isopropanol residue+0.2% by weight of polyethylene glycol.

(d) Isopropanol residue+0.2% by weight of polyethylene glycol dibutylether.

The above-mentioned fluxing agents contain no solid component such asrosin. It is, however, desirable to mix a solid component such as rosinin an amount of not larger than 10% by weight in an alcohol.

(a) Ethanol residue+2% by weight of hydrogenated rosin (Rika Hercules,Foral AX).

(b) Isopropanol residue+0.2% by weight of hydrogenated rosin (RikaHercules, Foral AX).

(c) Isopropanol residue+1.0% by weight of polymerized rosin (ArakawaKagaku, Dimerex).

(d) Isopropanol residue+1.0% by weight of gum rosin (Harima Kasei).

FIG. 21 illustrates the tenth embodiment of the present invention. Thisembodiment is the same as the embodiment of FIG. 20 except that afluxing agent vessel 96 is provided in the booth 82. The fluxing agentvessel 96 is supported by a table 97. It is desired that theabove-mentioned fluxing agent is applied in the booth 82, as shown inFIG. 21.

FIG. 22 illustrates an example in which a plurality of molten-soldervessels 84 a, 84 b, 84 c and a fluxing agent vessel 96 are arranged inthe booth 82 in the apparatus of FIG. 21. These molten-solder vessels 84a, 84 b, 84 c and the fluxing agent vessel 96 are placed on a rotarypallet 98, so that any one of them is positioned under the semiconductorelement 12 supported by the suction support device 90. By thisarrangement, plural kinds of solders can be successively transferred.

FIG. 23 illustrates a feature of the suction support device 90 in theapparatuses of FIGS. 20 and 21. The suction support device 90 includes asuction head 100 for supporting the semiconductor element 12 by avacuum, and a hanging mechanism 102 capable of holding the semiconductorelement 12 via the suction head 100. The suction head 100 is evacuatedthrough a vacuum hose 104, and suction grooves are formed in the surfaceof the suction head 100, so that the semiconductor element 12 issupported by the vacuum. The hanging mechanism 102 is mounted on aconveyer means that is not shown.

The hanging mechanism 102 comprises at least two mutually movablyconnected coupling members 102 a and 102 b. The coupling members 102 aand 102 b comprise two members coupled together as in a chain.

In FIGS. 20 and 21, when the semiconductor element 12 is lowered towardthe molten-solder vessel 84 so as to be immersed therein, the couplingmembers 102 a and 102 b of the hanging mechanism 102 are in contact witheach other in a supporting relationship. As the semiconductor element 12is lowered, the gold bump elements 62 are immersed in the molten-soldervessel 84 and the lower surface of the semiconductor element 12 is thenimmersed in the molten solder in the molten-solder vessel 84.

As the hanging mechanism 102 is further lowered, the coupling members102 a and 102 b can mutually, floatingly move and the semiconductorelement 12 is no longer supported by the hanging mechanism 102. Sincethe semiconductor element 12 has a specific gravity smaller than thespecific gravity of the molten solder the semiconductor element floatson the molten solder. Therefore, even if the hanging mechanism 102 isfurther lowered in excess of a position at which the semiconductorelement 12 is floating, the semiconductor element 12 does not receiveany force from the hanging mechanism 102 and is maintained in a floatingposition.

Therefore, the lower surface of the semiconductor element 12 becomesjust parallel to the surface of the molten solder in the molten-soldervessel 84, and the molten solder is uniformly transferred onto the goldbump elements 62.

FIGS. 24 to 26 illustrate modified examples of the hanging mechanism102. In FIG. 23, the two coupling members 102 a and 102 b are formed ascircular rings. In FIG. 24, the upper coupling member 102 a is formed asa circular ring, and the lower coupling member 102 b is formed as atriangular ring.

In FIG. 25, the upper coupling member 102 a is formed as a triangularring, and the lower coupling member 102 b is formed as a circular ring.In FIG. 26, the two coupling members 102 a and 102 b are both formed astriangular rings.

FIGS. 27 to 29 illustrate an embodiment of the pump-type suction head.The suction support device 90 of FIG. 23 has the suction head 100 whichis evacuated through the vacuum hose 104. The pump-type suction head100a shown in FIGS. 27 to 29 independently creates vacuum without theneed of connecting the vacuum hose 104. The suction head 100 a has acase 100 b, a piston 100 c and a piston rod 100 d. The piston rod 100 dprotrudes from an end of the case 100 b, and a suction hole 100 e isformed the other end of the case 100 b. The piston rod 100 d is providedwith an engaging projection 100 f which is inserted in an engaging hole100 f of an inverse L-shape formed in the outer periphery of the case100 b.

Referring to FIG. 29, when the piston rod 100 d is pulled with thesemiconductor element 12 being brought to one end of the suction head100 a, the piston 100 c rises in the case 100 b, whereby a vacuum iscreated in the case 100 b and the semiconductor element 12 is held bythe suction head 100 a. The engaging projection 100 f that arrives atthe vertex of the engaging hole 100 f of the inverse L-shape togetherwith the piston rod 100 d, enters into a horizontal portion of theengaging hole 100 f of the inverse L-shape. Therefore, the suction head100 a is maintained at a position of holding the semiconductor element12. The suction head 100 a can be used together with the hangingmechanism 102 of FIG. 23 or together with any other hanging mechanism orsupport mechanism.

FIGS. 30 to 32 illustrate examples where the suction head 100 a is usedtogether with the hanging mechanisms 102 of FIGS. 24 to 26.

The solder films can be formed on the gold bumps 62 attached to theelectrodes 14 of the semiconductor element 12, not only by immersing thegold bumps 62 in the molten solder, but also by vaporizing anddepositing the solder onto the gold bumps 62 as the solder films.

FIGS. 33 and 34 illustrate an example where the solder films are beingvaporized onto the gold bumps 62. In this case, a mask 106 havingopenings for exposing only the gold bumps 62 attached to the electrodes14 of the semiconductor element 12 is used. The semiconductor element 12with the mask 106 is introduced into a vacuum chamber 108, and a target110 is heated so that the solder vapor adheres onto the gold bumps 62.Thus, the solder films are deposited onto the gold bumps 62.

As described above, the present invention provides a semiconductordevice and a method and an apparatus for producing the same which enablea semiconductor element to be mounted to the wiring board by a face-downtechnique and which provide for improved reliability in the connectingportions and simplicity of the replacement of the semiconductor element.

What is claimed is:
 1. A method of producing semiconductor devices,comprising the steps of: attaching gold bump elements to electrodes of asemiconductor element; immersing said semiconductor element in a bathcontaining a molten amalgam of a mixture of a metal for protecting goldand of mercury to form an amalgam layer on said gold bump elements;heating said semiconductor element to vaporize the mercury in theamalgam and to form metal films on the gold bump elements to protectgold, and transferring molten solder elements to said metal films.